There are some curses in the (later) game which can really wreck your day. I would never go without the ability to remove them. I like to have Shadowheart in the group, firstly she looks good and secondly as Cleric she can swap all spells as she likes and does not need to learn the curse removing spell, other than Gale. At least one of them should have it.
Not having a good lockpick character hurts, too. Sometimes it can shut you out of quests (although mostly there are means to circumvent locked doors). My group is currently Sorceress, Shadowheart, Gale and Minsc, and sometimes I miss Astarion. My best lockpicker is Minsc (Barbarian), however not as good as Astarion. For my taste there should be at least a bonus of +10 to lockpicking before applying other buffs from Cleric or so.